OPTICAL POWER LIMITING WITH SOLUTIONS OF HEXAGONAL PRISM CAGE-SHAPED TRANSITION-METAL CLUSTER MO2AG4S8(PPH(3))(4)

We report the optical limiting responses of a hexagonal prism cage shaped transition metal cluster Mo2Ag4S8(PPh(3))(4) in acetone and acetonitrile solutions to 8-ns laser pulses. We have observed that the limiting behavior occurs in the entire visible spectrum. The limiting performance of the cluster is 1 order of magnitude better than that of a C-60-toluene solution at a wavelength of 532 nm. The nonlinear absorption and refraction responsible for the Limiting effect are effectively irradiance dependent. The possible underlying mechanism is discussed. With the Z-scan technique, we have determined the effective third-order absorptive and refractive nonlinearity (alpha'(2) and n'(2)) to be (1.0 +/- 0.4) x 10(-3) L cm W-1 mol(-1) and (1.2 +/- 0.5) x 10(-8) L cm(2) W-1 mol(-1), respectively, at 532 nm.